System and method for registering motion picture film

ABSTRACT

A system and method for registering the frames of film with respect to an aperture in a motion picture projector. A registration reference mark is applied to each frame corresponding to the location of the frame on the film. When the film is intermittently stopped in the projector&#39;s film gate, the registration reference mark is read to determine the location of that frame relative to the immediately preceding frame. If the frame in the gate is misregistered, the gate is moved to correctly register the frame prior to projection. By properly registering the frames, the “jitter” and “weave” associated with conventional projectors is eliminated and resolution of the projected film image is enhanced.

This is a continuation of application Ser. No. 10/669,984, filed on Sep.24, 2003, which is a continuation of application Ser. No. 10/242,037,filed on Sep. 10, 2002, which is a continuation of application Ser. No.09/481,602, filed on Jan. 12, 2000, which is now issued as U.S. Pat. No.6,450,644, issued on Sep. 17, 2002.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to motion picture filmregistration techniques and, more particularly, to a system and methodfor correctly registering frames of motion picture film during theprojection process to provide enhanced resolution of the projectedimages.

2. Description of the Related Art

Film projectors and the motion pictures they project have amazed anddelighted audiences around the world for over a century. However, theterm “motion pictures” is really a description of an illusion, for thepictures do not actually move at all. To the contrary, still images,typically 24 per second, must be projected in as static a manner aspossible. This is not a simple proposition given the fact that in oneminute 1,440 images or “pictures” are presented to the viewer. Theillusion of motion is created by the differences between succeedingstill images and is dependent upon the precise positioning or“registration” of these images with respect to an aperture in theprojector.

One of the problems associated with existing motion picture filmprojectors occurs when succeeding images are positioned in slightlydifferent locations in the projector's aperture. When this happens, agiven point on those images will appear to be blurred, even ifindividual images show that point to be perfectly sharp. Of course,individual images in motion pictures are not viewed separately, but,rather, over time in rapid succession.

In the context of motion picture technology, the word “register” (theroot for “registration”) is not formally defined. Perhaps the closestapplicable general definition is provided in the Random House DictionaryOf The English Language, Second Edition Unabridged (1983): “(11b) Print.Correct relation or exact superimposition, as of colors in colorprinting.” In the art of motion pictures, however, “registration” has aslightly different meaning. Motion picture photographic “registration”means the repeated placement of each image, one after another, in asprecise a manner as possible throughout the entire chain that comprisesthe system of cinema imaging. As described below, there are severalsteps in this chain, starting with creation of the image and ending withits projection.

At the outset, film is moved through the camera intermittently andpositioned by “registration pins” in precisely the same place, calledthe “aperture”. In this way, a succession of areas called “frames” areexposed to light, thus creating “latent images” that become a visibleimage after development. Because the “frame” defines the rectangularspace on the film that is occupied by the “image,” the terms “frame” and“image” shall be used interchangeably and synonymously with each otherherein.

During editing and other post-production processes, images created inthe camera are modified when appropriate. Then they are duplicated fordistribution through a process that involves intermediate steps. Theseintermediate steps include contact printing of an inter-positive (“IP”),and using that IP to make inter-negatives (“IN”).

In the next step, the IN is transferred onto release print film viahigh-speed contact printing, which is an unregistered process thatoperates at up to 17×-play speed, or faster. The “release prints” madeby this process are distributed to theaters for projection. When therelease prints are projected, the frames are intermittently positionedin a fixed position relative to the “aperture” of a projector's “gate.”Light from a lamphouse in the projector projects the images onto ascreen for viewing by an audience.

Registration is not a factor in creating high resolution stillphotographic images. The photographer and viewer of a still photographare concerned only with a single image recorded and printed from asingle piece of film containing that image. However, registration is acrucial component required for high resolution imaging in motionpictures. As noted above, motion pictures are dependent on thousands ofimages seen one after another in rapid succession. Thus, in motionpictures, the collective impression of resolution or sharpness is highlydependent upon the repeatable, accurate positioning in the projector ofevery image that is photographed and projected.

“Resolution” is another term for sharpness or clarity. In motionpictures, resolution is a function of several factors, which include:(1) lens sharpness; (2) film negative granularity; (3) repeatable,accurate registration of the film in the camera's aperture; (4)repeatable, accurate registration during exposure of film IP's, IN's,and release prints; (5) film print granularity; and (6) repeatable,accurate registration of the release print in the projector. Of allthese factors, nos. 4 and 6 are the most severely flawed in currentmotion picture technology. According, a long-felt need has existed for asystem and method that can address these factors and thereby providemore precise registration and enhanced resolution across the entiresystem of motion picture imaging.

The final measurement of motion picture resolution must be made byanalysis of a projected image at 24 frames per second (standard) orfaster, not by inspection of individual frames as with stillphotography. Ideally, the registration precision of the projector shouldmatch that of the camera. Unfortunately, that is not now and never hasbeen the case. As noted above, motion pictures cameras use highlyprecise, mechanically activated “registration pins” to achieve andmaintain final and repeatable film positioning from frame to frame. Onthe other hand, theatrical projectors use registration techniques thatare, at best, considerably inaccurate about both the longitudinal andlateral axes. This inaccuracy gets progressively worse as variousmechanical parts in the projector's intermittent movement and gate aresubjected to normal wear over time. But the primary cause of thisinaccuracy is the 100-year-old design of the projector movement itself.Projector gates, intermittent sprockets, and the “Geneva” mechanism thatturns these sprockets in a pause-then-rotate cadence have failed toevolve in any meaningful manner.

As described more fully below, projector registration in its presentstate is primarily achieved by means of the friction provided by springtension in the projector gate, acting against the film, which isadvanced by the rotational movement of the intermittent sprocket. Thisintermittent sprocket is typically positioned about 2 to 4 inches ormore below the aperture and pulls the film through the gate. When theintermittent sprocket stops pulling the film, the spring tension in thegate acts on the film sandwiched within it and friction causes the filmto stop. But this is a highly passive design that lends itself toimprecision. For example, gate friction varies due to adjustable springtension. Moreover, the film print itself exhibits variable “slickness”due to waxing, wear and other environmental factors. Therefore, eachsucceeding frame simply cannot be registered in the exact same locationas the preceding frame.

During projection, inaccurate longitudinal registration of the filmproduces an up and down film movement called “jitter,” while inaccuratelateral registration produces a side-to-side film movement called“weave.” Both jitter and weave are greatly magnified by the extremeenlargement of projection. At a minimum, jitter and weave in anynoticeable amount will result in a softening and blurring of detail andimpair the resolution of the projected images.

The use of larger images on film, as with the various 70 mm formats,creates a sharper image on screen simply because less enlargement isrequired to fill the screen. Consequently, the jitter and weave of theimage is less noticeable with 70 mm release prints. However, the highercost and the lack of 70 mm projectors in most theaters renders thevarious 70 mm formats moot as an option, except in a few “special venue”theaters. Indeed, if jitter and weave in the 70 mm projectors could bereduced or eliminated, the projected image would be even sharper.

Current theatrical motion picture projectors inherently create jitterand weave because they lack any kind of positive film registrationtechnology. Furthermore, the high-speed printing process used tomanufacture most IP's and IN's and thousands of release printsdistributed to theaters creates yet another level of jitter and weave initself. In order to understand the problems that this causes when thefilm is finally projected, it is necessary to understand how motionpicture images are photographed.

In a typical camera movement, film is driven from the camera magazine bya constant speed sprocket, which maintains an upper loop of film. Apulldown claw driven by an eccentric cam-like movement penetrates thefilm's perforations and pulls the film into precise registration in thecamera's aperture. The upper loop, much of which is taken up for thisoperation, is replenished by the continuous rotation of the constantspeed sprocket. Next, with the film stopped, the registration pinspenetrate adjoining perforations in the film, while simultaneously thepulldown claw retracts and begins moving back into position to take holdof the next length of film to be pulled down. Meanwhile, as theregistration pins penetrate the film's perforations, their tapered teethgently move the film into precise position. The registration pins arerestricted to a simple back and forth movement and are locked in apredictable, repeatable accurate mechanical design. Also, theregistration pins are located immediately adjacent to and oftensurrounding the portion of the film to be exposed. For these reasons,they are very accurate and allow the camera to expose a continuoussuccession of images in precise registration.

In a typical projector movement, however, there is very littlesimilarity to camera movements. Although a typical projector has aconstant speed sprocket that feeds film to maintain an upper loop, allsimilarity to cameras ends at that point. Unlike a camera, the film'sadvance into the projector gate is provided by a powerful pull from anintermittent sprocket positioned below the projector gate's aperture,through which light is passed during projection. The projector gate is agently curved, spring tensioned “trap” that exerts friction on the filmand thus acts in opposition to the motive force that pulls film throughit. When the intermittent sprocket stops pulling the film through thegate, the friction exerted by the gate stops the film. Unfortunately,this mechanism cannot duplicate the precise registration provided bycameras for several reasons.

First, the gate's friction, as applied to the movement of the film, isadjustable and varies from projector to projector. Higher frictionprovides heightened opposition to the film's intermittent movement, butsimultaneously demands that more torque be applied to overcome thisstatic friction for frame-to-frame advance. This can cause filmstretching or, in extreme cases, breakage. Also, gate friction that istoo high may cause so much film resistance that the teeth of theintermittent sprocket will deform the perforations in the film duringpulldown, which leads to deteriorating registration in every subsequentshowing of the film. But if gate friction is reduced too much, the filmmay continue moving slightly after the rotation of the intermittentsprocket stops. In these cases, the film overshoots the proper locationin a way that is prone to be erratic from frame-to-frame.

Second, film prints are often waxed or otherwise provided with a slicksurface in order to slide through the gate with reduced resistanceand/or to help prevent stretching of the film. This prevents the filmfrom stopping in the gate in precisely the same place from one frame tothe next.

Third, film often shrinks or expands due to age, humidity and otherfactors. Thus, the distance from the image in the aperture to theintermittent sprocket necessarily varies. The effect of such shrinkageor expansion increases with greater lengths of film. Therefore, thedistance between the aperture and the intermittent sprocket includesfurther margin for error.

Fourth, the mechanism that advances the intermittent sprocket is drivenby a “Geneva” movement, which is subject to wear. The Geneva movement iswell known and comprises a “Maltese” cross-shaped device, with slots cutinto each cross. A rotating cam-like device turns within it, with a pinthat engages the slots in the cross. This produces a pause-then-rotateintermittent movement, which is then applied to a shaft connected to theintermittent sprocket that pulls the film through the aperture frombelow the gate. Although the Geneva movement turns in an oil bath thatis designed to inhibit metal-to-metal contact, like any mechanicaldevice, there is always some wear. This wear causes slight imprecisionin the application of the motive power to the connecting shaft, theintermittent sprocket and the film itself, which is then magnified bythe act of projection.

Fifth, the slightest bend in the shaft connecting the Geneva movement tothe intermittent sprocket will impart an eccentric movement to theintermittent sprocket, so that instead of rotating in a circularmovement, it will rotate in a slight oval-shaped pattern. This in turnexacerbates any imprecision in the Geneva movement, which, in turn,impairs resolution of the projected image.

Finally, release prints are made on non-registered, high-speed printersthat introduce additional imprecision by placing the images in differentpositions with respect to the film edges and perforations. In otherwords, this non-registered printing process microscopically misplacesframes in such a way that they are no longer located in a precise,repeatable relationship to the edges and perforations of the film.

Certain special-purpose, pin-registered projectors have been built for atype of special effects cinematography called “process shots,” but theseprojectors were not designed for theatrical projection. Instead, theywere designed to achieve precise registration with the assumption thatthey would be showing prints made on some type of relatively slow,highly accurate printer, rather than release prints duplicated byhigh-speed, non-registered contact printers.

Two new projector designs have recently appeared for 70 mm special-venueapplications that provide some equivalent of pin registration. TheMega-Systems projector has two intermittent sprockets, placed both aboveand below the aperture. A curved, one-sided gate mechanism is broughtinto intimate contact with the film by sliding back toward it. Thisdesign is intended to allow for film shrinkage or expansion while stillproviding positive registration. The Linear Loop projector by IWERKSseeks to achieve the equivalent of positive pin-registration by usingblasts of controlled, compressed air to advance film across a parallelset of linear sprockets placed on either side of the projector'saperture. These linear sprockets, which are analogous to railroadtracks, hold the film's perforations as succeeding frames are advancedby means of a “standing wave” of film that rolls across the sprockets,propelled by the air blast. Though these two projectors provideregistration that duplicates, somewhat, the positive registration foundin cameras, they do not address the misalignment created bynon-registered high-speed contact printers.

In another area of motion picture technology called “telecine,” wheremotion picture images are transferred to videotape, various methods havebeen developed to achieve a stable image. While there are differences inthe devices and methods used to achieve image stabilization in thesetelecine-based systems (sometimes called “electronic pin registration”),they all have one thing in common—they all seek to stabilize the filmimage by reference to the film edges and/or perforations on the film.This is acceptable in telecine, because telecine uses “low contrast”prints that are made at 180 feet per minute in “wet gate” contactprinters. Thus, the image position on low contrast prints used intelecine bears a relatively accurate relationship to the film's edgesand/or perforations. However, the technique of using the edges and/orperforations on release prints as a reference to stabilize the filmimage wrongly assumes that the images on the film are correctlyregistered with respect to the edges and perforations, as they are inthe camera or with prints made on relatively slow, highly accurateprinters. As discussed above, theatrical release prints are made onnon-registered contact printers at speeds often in excess of 1,500 feetper minute. This high-speed, non-registered printing processmicroscopically misplaces frames in such a way that they are no longerlocated in a precise, repeatable relationship to the edges andperforations of the film.

While various types of electronic pin registration and/or imagestabilization methods and technologies work well when scanning printsmade on registered printers, they cannot correct for improper placementof the image relative to the edges and/or perforations of the film. Asdiscussed above, such improper placement is a common occurrence due toerrors engendered in high-speed contact printing of theatrical releaseprints. Consequently, electronic pin registration has limited value fortheatrical projection. In fact, none of these systems were designed withthat purpose in mind. Rather, they all declare to be directed toward theprocess of scanning film to video or digital electronic form.

Accordingly, there has existed a definite need for a system and methodthat can achieve precise image stabilization and enhanced resolution fortheatrical motion picture film projection, that corrects formisplacement of images on the release print film (compared to theoriginal negative), and which does not rely on the edges of the film orits perforations to do so. The present invention satisfies these andother needs and provides further related advantages.

SUMMARY OF THE INVENTION

The present invention provides a system and method for preciselyregistering frames of film with respect to an aperture in a motionpicture film projector. The projector comprises a gate for receiving andguiding film during intermittent advancement of the film through theprojector. In accordance with the invention, information is applied tothe film corresponding to the location of the frames on the film. Theinformation associated with each frame is read by a sensor prior toprojection to determine the location of the frame with respect to theaperture. If the frame is misregistered with respect to the apertureonce the film stops in the gate, an actuator moves the film relative tothe aperture to achieve the correct registration. By repeatedlyregistering the frames in the exact same location with respect to theaperture, the resolution of the projected motion picture image issubstantially and advantageously enhanced.

In conventional projector designs, the gate is connected to theprojector in a fixed manner relative to the aperture. In accordance withone embodiment of the present invention, however, the gate is adapted tomove relative to the aperture. Movement of the gate relative to theaperture is provided by an actuator connected to the gate. In one formof the invention, the actuator comprises a piezoelectric motor or amoving coil motor. Both of these types of motors can be used inconjunction with a flexure stage to provide the required gate movement.The actuator preferably is configured to move the gate in increments assmall as approximately 0.000002 inches in about 1 millisecond or less,depending on the frame rate. In addition, the actuator and the gate areconfigured such that the actuator can move the gate at least about 0.006inches in both the X direction and the Y direction.

The information necessary to move the gate by the required amount isprovided by the registration information applied to the film. In oneform of the invention, the registration information comprises aregistration reference mark that is capable of being read by a sensor.The registration reference mark preferably comprises a plurality ofdifferent shapes that are read by the sensor. In one aspect of theinvention, the plurality of different shapes comprises at least a circleand a square or rectangle, where the diameter of the circle is equal tothe width of the square or rectangle. In addition, a triangle may bepositioned adjacent to the circle and the square or rectangle to providefurther registration information.

The registration information is applied to the film in the same locationrelative to each frame. In this regard, the registration informationpreferably is located on the film in an area outside the frame, and,most preferably, the registration information is located in the spacebetween adjacent frames. Furthermore, if desired, redundant registrationinformation may be applied to the film for each frame.

The sensor that reads the registration information on the film may takea variety of forms. In one embodiment, the sensor comprises alight-based sensor. For example, the sensor may comprise an LED array onone side of the gate that transmits light through the registrationreference mark on the film. The transmitted light is received by a CCDarray on the other side of the gate. If desired, one or more mirrors maybe used to reflect the light transmitted from the LED array onto the CCDarray. In addition, redundant sensors may be used to read redundantregistration information associated with each frame.

A registration processor controls the operation of the sensor andprocesses the registration information for each frame to determine thelocation of each frame with respect to the aperture. The location ofthese frames is determined by reading the registration informationassociated with each frame. The registration processor then uses theregistration information to compare the location of a frame in the gaterelative to the immediately preceding frame. If a frame is not properlyregistered with respect to the aperture in the same place as theimmediately preceding frame, then the registration processor calculatesthe amount of film misregistration. Based on the amount ofmisregistration, the registration processor generates an appropriateoutput signal that is delivered to the actuator. This output signalcommands the actuator to move the gate in such a manner that the frameis correctly registered relative to the immediately preceding frame. Inthis way, each of the frames will be registered in the same locationrelative to the aperture. The output signal may comprise a voltage-basedsignal, a current-based signal, or other suitable signal configured tomove the actuator and thus the gate.

Other features and advantages of the present invention will becomeapparent from the following detailed description, taken in conjunctionwith the accompanying drawings, which illustrate, by way of example, theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate the invention. In such drawings:

FIG. 1 is a diagrammatic representation of the six degrees of freedomfor defining any location in three-dimensional space.

FIG. 2 is a schematic view of film travelling through a motion pictureprojector.

FIG. 3 is another schematic view of film travelling through theprojector, showing the maximum amount of roll of the film in theprojector gate.

FIG. 4 is an elevational side view of a conventional motion picture filmprojector, showing film travel through the projector.

FIG. 5 is a schematic view showing the position of the projector gaterelative to an aperture of the projector.

FIG. 6 is a schematic view of a piezo crystal according to oneembodiment of the present invention.

FIG. 7 is a graph depicting the relationship between applied voltage andthe length of the piezo crystal.

FIG. 8 is a schematic illustration of a piezoelectric motor flexurestage, shown partly in cut-away section, used to move the projector gateand correct for film frame misregistration, in accordance with oneembodiment of the invention.

FIG. 9 is a schematic illustration of a moving coil motor used to movethe projector gate, in accordance with another embodiment of theinvention.

FIG. 10 shows a registration reference mark according to one embodimentof the invention.

FIG. 11 is a section of film showing the location of a registrationreference mark between the frames of the film.

FIG. 12 shows a matrix CCD array according to one embodiment of theinvention.

FIG. 13 shows a line CCD array according to another embodiment of theinvention.

FIG. 14 is a rear elevational schematic view of a projector gate andassociated projector structure embodying the novel features of thepresent invention.

FIG. 15 is a side elevational view of the projector gate and associatedprojector, taken along the line A-A of FIG. 16.

FIG. 16 is a front elevational view of the projector gate and associatedprojector structure, similar to FIG. 14.

FIG. 17 shows selected portions of a registration reference markaccording to one embodiment of the invention.

FIG. 18 shows additional aspects related to the registration referencemark.

FIG. 19 shows another selected portion of the registration referencemark, including reference lines for calculation of framemisregistration.

FIG. 20 is a schematic illustration of one alternative for illuminatingthe registration reference marks.

FIG. 21 is a schematic illustration of another alternative forilluminating the registration reference marks.

FIG. 22 is a block diagram showing a registration processor and otherrelated processor components in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with the present invention, film frame misregistration isdetected and corrected on a frame-by-frame basis to ensure preciseregistration of each frame with respect to the projector's aperture. Byregistering each frame in the same position with respect to theaperture, the resulting motion picture, comprised of these individualprojected images, has dramatically enhanced resolution. Proper frameregistration is achieved, and misplacement of images on release printfilm is corrected, by making corrective film movements while the film isintermittently stopped in the projector gate. As explained below, thisprecise film registration and the resulting enhanced film resolution isprovided by making corrective film movements in only two directions,corresponding to the X direction and the Y direction.

In this regard, and by way of further background, any type of motion canbe described with reference to six degrees of freedom. As shown in FIG.1, these six degrees of freedom comprise three degrees of linearmovement commonly known as X, Y and Z, and three degrees of angularmovement commonly known as yaw, pitch and roll. Because film is flat,and because of the way it is captured in the projector gate, there canbe no discernable yaw or pitch movements of the film. Although there issome thermal shock defocusing of the film in the Z direction, due to theheat absorbed by the film from the projector's lamphouse, which causesthe film to deflect slightly, any movement in the Z direction isconsidered to be a very minor aspect of misregistration, as compared tothe misregistration of the film in the X and Y directions.

Further, while it is possible to correct for possible misregistrationdue to roll, the magnitude of this movement is also considered to berelatively small. In this regard, as shown in FIG. 2, film 10 thattravels through the gate is mechanically guided past the aperture 12over a long distance compared to the width of the film. In mostprojector designs, the film 10 is guided by mechanical guide means 14,such that the film has the capacity to deviate in the gate in the Xdirection by only about 0.003 inches. As shown in FIG. 3, film 10 thatmoves by this amount would result in a maximum roll component of onlyabout 0.049 degrees. This small angular rotation component is relativelyinsignificant and is unlikely to have any noticeable impact onresolution. Thus, the necessity and cost of correcting it is subject toquestion.

In view of the foregoing, and the fact that jitter and weave are themost significant factors that contribute to film misregistration, thesystem and method of the present invention is designed to detect andcorrect film misregistration in the X direction (weave) and the Ydirection (jitter). It should be understood, however, that theprinciples of the invention can be applied to detect and correct filmmisregistration in other directions as well. Therefore, the descriptionthat follows should not be construed as limiting the invention tocorrect misregistration in the X and Y directions only.

Referring to FIG. 4, a typical 35 mm projector 16 has two constant speedsprockets, comprising a feed sprocket 18 and a hold-back sprocket 20,located on opposite sides of a film gate 22. An intermittent sprocket 24is also located between the gate 22 and the hold-back sprocket 20,approximately two to four inches (or more) below the gate. Theintermittent sprocket 24 pulls the film 10 intermittently, frame byframe, through the film gate 22 in a well-known manner. Slack in thefilm 10, in the form of loops of loose film 26 and 28, is provided,respectively, between the feed sprocket 18 and the film gate 22 andbetween the intermittent sprocket 24 and the hold-back sprocket 20 toprevent film breakage.

The film gate 22 also includes an aperture plate 30 with an aperture 32designed to be in optical alignment with a projection light source 34(such as a lamp house) on one side of the gate and a lens 36 on theother side of the gate. A rotating shutter blade (not shown) between theaperture 32 and the lamp house 34 blocks light from the lamp houseduring pull down and registration of the film 10 and permits passage oflight through the aperture upon registration of a frame 40 with respectto the aperture. The shutter blade or counter-rotating blades arerotated in a well known manner by a shutter motor (also not shown).

The gate 22 serves several functions during the projection process. Oneof these functions is to mechanically guide the film 10 through theprojector 16. In this sense, the gate 22 acts as a mechanical alignmentsystem, whose purpose is to control film movement in the X direction or“weave.” The weave present in today's projectors primarily occurs as aresult of variations in film width and mechanical deviations in the gatewidth.

Another purpose of the gate 22 is to apply friction to the film 10,which stops the film in the gate when the intermittent sprocket 24 stopspulling the film. In this context, the gate 22 is mechanically similarto a constant drag system and must have drag components large enough toquickly stop the film 10. Although the film 10 does not create a largeinertial force, because film is a light material and there is only asmall amount of it moving when the intermittent sprocket 24 advances thefilm, a static friction of up to several pounds is still required toovercome this inertia effect and stop the film. As betweenmisregistration of the frames 40 in the X direction and the Y direction,however, misregistration in the Y direction is usually the largest ofthe two.

Because the gate 22 in conventional projectors is designed to registerthe frame 40 with respect to the aperture 32, the gate is an importantaspect of the film registration process. However, for the reasonspreviously explained, it is virtually impossible for conventionalprojector gate designs to precisely register the frame 40 in properalignment with the aperture 32. Accordingly, to correct for thisconstant misregistration from one frame to the next, the system andmethod in accordance with one embodiment of the present invention isdesigned to physically move the gate 22, after the film 10 has beenstopped in the gate by friction, to precisely register the frame 40 withrespect to the aperture 32.

FIG. 5 schematically illustrates the position of the gate 22, which, inaccordance with the invention, is moveable in the X direction and the Ydirection relative to the aperture plate 30 of the projector 16 and itscorresponding aperture 32. The intermittent sprocket 24 is located belowthe gate 22 and is driven by an intermittent motor 38. In conventionalprojectors, as shown in FIG. 4, the gate 22 is attached to the projector16 in a fixed position and therefore does not move. In accordance withthe present invention, however, the gate 22 is configured so that it canbe moved to provide for the necessary corrective movements that willresult in precise registration of the frame 40 with respect to theaperture 32. In the preferred embodiment, the gate 22 is configured tomove in the X direction and the Y direction, as necessary, to preciselyregister the film 10.

The range of gate movement in the X and Y directions preferably issufficient to allow enough movement in each direction to correct for a“worst case” situation of misregistration. A worst case situation isbelieved to be a maximum deviation of about +/−0.003 inches, although itcould be more or less than this amount. Therefore, to correct for thesedeviations, the gate 22 should be able to move at least about 0.006inches in both the X direction and the Y direction. However, it will beunderstood that a larger range of gate movement is possible and that theinvention is not limited to the specific ranges of movement set forthherein. In any event, in order for the range of gate movement to be ableto provide enhanced resolution through precise frame registration, thecorrective movements of the gate 22 preferably should be at a level andin increments that are at least on par with the obtainable film grainresolution available.

According to today's standards, typical film 10 has the capacity toresolve approximately 4,850 lines per inch in any axis. In order tocorrect misregistration and project an image as a steady picture, gatemovement should ideally be at least ten to one hundred times moreprecise than the smallest film grain size. Gate movement at this levelof precision would not only allow the system to accurately position oneframe relative to the next, but it would also allow for futureimprovements in film stock technology. Accordingly, in one aspect of theinvention, gate movement preferably can move the film in increments of{fraction (1/20)} of a micron, or 0.000002 inches.

Movement of the gate 22 to correct misregistration of the film 10preferably occurs during the period in which the film is stopped, afterthe pull down from the intermittent sprocket 24 and before the shutteropens. During this period of time, several operations must be performed.As explained in more detail below, these operations include determiningthe position of the film frame 40 relative to the previous frame,calculating the amount of corrective gate movement, and then moving thegate 22 accordingly.

Because the frames 40 will be registered at a rate of at least 24 framesper second (i.e., one frame about every 41.6 milliseconds), all of theseoperations, and particularly the movement of the gate 22, needs to beperformed as quickly as possible. Movement of the gate 22 isaccomplished mechanically and, therefore, is subject to certain physicallimitations. Of course, the shutter will not open until the film 10 hasbeen pulled down and stopped in the gate 22. If the amount of time topull down each frame 40 is approximately 8.0 milliseconds, then theoperations necessary to move the gate 22 and register the frame 40 mustbe performed in approximately 2.5 milliseconds after the film 10 hasstopped and before the shutter opens. By allowing approximately 1.5milliseconds to determine the location of the frame 40 and to calculatethe amount and direction of corrective gate movement necessary, there isapproximately 1.0 millisecond of time remaining to actually move thegate 22. If the frame rate is 48 frames per second, then the amount oftime to move the gate 22 will be the same as those set forth above.Similar calculations can be made to budget the proper amount of time tomove the gate 22 based on other frame rates that may be used.

In order to move the gate 22 within the time available to do so, theinertia of the gate ideally should be as small as possible. Accordingly,the intermittent motor 38 should not be attached to the gate 22, and theaperture plate 30 should remain fixed relative to the lens 36 andintermittent motor 38, with the gate 22 moving independently of both.The actual configuration to permit the gate 22 to move can beaccomplished in several ways, so long as it has the freedom to move atleast about 0.006 inches in the X and Y directions. For example, flexurestages, bearings, slides, and other suitable configurations can be usedin conjunction with an appropriately configured gate 22.

In order to move the gate 22 by the distance necessary to accuratelycorrect frame to frame misregistration, a movement mechanism isconnected to the gate. This gate movement mechanism is referred toherein as an “actuator.” Given the gate movement parameters discussedabove, the actuator must be able to move the gate 22 rapidly (i.e., inabout one millisecond or less). The actuator also must be able to movethe gate 22 in a precise manner (i.e., preferably in increments of0.000002 inches). An actuator capable of meeting these gate movementparameters may take several different forms. For example, it maycomprise a system that utilizes fluids, air pressure, mechanical devicesor electromechanical devices to provide the required movement. Of theseoptions, electromechanical devices are presently preferred, due to thehigh level of control and the higher speed response that they provide.

Electromechanical devices come in many different forms, such as rotaryor linear motors, piezoelectric motors, bi-material actuators, and otherdevices that change shape or size based upon an electrical influence.Rotary motors represent a common system that transfers rotary motioninto linear motion through the use of a screw, cam or similar device.Linear motors, such as moving coil motors or speaker coil motors, arealso candidates for the actuator due to their precise movements andquick response time. Bi-material actuators rely upon the dissimilarnature of two materials to cause a bowing or shape change that can beconverted into precise linear motion. Of these options, piezoelectricmotors or moving coil motors are presently preferred actuators.

The piezoelectric motor has several attributes that make it a verycapable actuator. Among these attributes are the piezoelectric motor'shigh speed capability and its high positional accuracy. In fact,accurate moves in increments as small as one nanometer (i.e., onebillionth of a meter), or less, can be achieved, provided propermechanics and electronics are employed.

As shown schematically in FIG. 6, a piezoelectric motor 42 employs apiezo crystal 44 that increases or decreases in length in proportion tothe voltage that is applied across the crystal. When the voltage acrossthe crystal 44 is increased, the length of the crystal increases,whereas reduced voltage decreases crystal length (see FIG. 7). Oneadvantage of using the piezoelectric motor 42 as the actuator is that itis not necessary to have a feedback loop or to constantly monitor theactual position and the commanded position of the gate 22. Feedbacksystems of this nature are commonly deployed in motor controlapplications and would be required if a moving coil motor (discussedbelow) is used as the actuator.

By eliminating the feedback loop, the amount of microprocessor powerrequired by the piezoelectric motor 42 to both initially move the gate22 and then keep it in the correct position during the time the shutteris open is reduced. Moreover, piezoelectric motors 42 have a highlyreliable and predictable move distance based upon the applied voltage.As noted above, and as represented in FIGS. 6-7, voltage applied to thepiezo crystal 44 causes it to increase or decrease by a very precisedistance in a linear manner along the axis of the crystal. Therefore, asimple calculation or the use of available conversion tables willindicate the exact amount of voltage that must be applied to increase ordecrease the length of the crystal 44 by any given distance with veryhigh accuracy. While piezo crystals 44 are known to have a reboundaffect, this effect occurs over an extended period of time and does notstart to occur until at least several seconds have passed. Therefore,the rebound effect of the crystals is a very small factor because thetime period between each corrective move is so small.

In one form of the invention, the piezoelectric motor 42 comprises ahigh-resolution piezoelectric motor flexure stage 46. As shownschematically in FIG. 8, the stage 46 comprises two piezoelectric motors42 protected by an outer metal frame 48. The peizoelectric motors 42have one end connected to the outer frame 48, which is fixed againstmovement, and another end connected to an inner frame 50 that ismoveable with respect to the outer frame 48. As explained later inconjunction with FIGS. 14-16, the moveable inner frame 50 is connectedto the projector gate 22, and the fixed outer frame 48 is connected to asuitable fixed structure of the projector 16 that surrounds the gate.

The stage 46 also includes a plurality of flexures 52, which arefrictionless, stictionless devices that rely upon the elasticdeformation or “flexing” of a solid material. The flexures 52 areconnected between the outer frame 48 and the inner frame 50 andadvantageously eliminate sliding and rolling. These flexures 52essentially act like springs that bias the moveable inner frame 50 withrespect to the fixed outer frame 48. They are capable of providing thesmall increments of movement in response to the linear motion of thepiezoelectric motor 42, in accordance with the principal of materialelastic flexing, to provide mechanical movement translation. Theflexures 52 are also particularly advantageous because they eliminatethe common linear path errors associated with linear bearings.Therefore, such flexure-type positioners are superior to traditionalpositioners, such as ball bearings, cross roller bearings, etc., interms of resolution, straightness and flatness.

The peizoelectric motor flexure stage 46 is preferably equipped with atleast two piezoelectric motors 42. The flexure stage 46 also may beprovided with two high-resolution capacitive displacement sensors 54,but they are not required. The piezoelectric motors 42 provide themotion required to move the gate 22 with sub-nanometer resolution in theX direction and the Y direction. The capacitive displacement sensors 54comprise a probe 56 and a slightly larger target plate 58. The sensors54 also have sub-nanometer resolution and insensitivity to lateralmotion. Digital control electronics connected to the stage 46 by a cable60 can evaluate the combined information of the capacitive displacementsensors 54 and transform that information into two individual signalsproportional to X and Y linear displacement.

High resolution piezoelectric motor flexure stages 46 of the typedescribed above, and which have the capability of moving the gate 22 bythe required range of motion, and in the required increments, arecommercially available and can be obtained from, for example, PhysikInstrumente GmbH & Co., Polytec Platz 1-7, 76337 Waldbronn, Germany.Piezoelectric motor flexure stages 46 available from this company canprovide sub-nanometer movements and virtually unlimited resolution thatis not limited by stick-slip effects or by threshold voltages. Thesestages 46 also have piezoelectric motors 42 that have an extremely fastexpansion and thus provide an extremely fast responding positionalelement, with microsecond time constants. Furthermore, the piezoelectricmotors 42 in these stages 46 have the further advantage that they aresolid-state. Thus, they require no maintenance and are not subject towear and tear.

A moving coil motor 62 also may serve as a suitable actuator. The movingcoil motor 62 uses a system very similar to a speaker. As shownschematically in FIG. 9, the moving coil motor 62 comprises a magnet 64and a wire coil 66 surrounding the magnet. Like the piezoelectrictransducer flexure stage 46 discussed above, the moving coil motor 62also may be used in conjunction with a flexure stage having a pluralityof flexures and high-resolution capacitive displacement sensors,including a probe 68 and a slightly larger target plate 70 to determineposition. The wire coil 66 is connected to the inner frame 72 of theflexure stage that, in turn, is connected to the projector gate 22. Themagnet 64 is stationary and fixed to the surrounding metal outer frame74 of the stage. In use, current is passed through the wire coil 66. Byvarying the intensity of the current, the wire coil 66 will be movedrelative to the stationary magnet 64 until an equilibrium is met betweenthe stage flexures and the force of the magnet pull. In this way, theinner frame 72 of the stage and thus the gate 22 will be moved withrespect to the outer frame 74 to properly position the gate 22 andregister the frames 40 of the film 10.

The actuator preferably is moved or driven in a linear manner by anactuator driver. The actuator driver may comprise any suitablearrangement that allows control over the actuator in response to eithera straight analog signal, a digitally processed signal, or anothersuitable signal. When the piezoelectric motor 42 serves as the actuator,the actuator driver comprises a voltage controlled system. If the movingcoil motor 62 serves as the actuator, then the actuator driver is acurrent controlled system. Other suitable types of actuator drivers willbe apparent and can be selected based on the type of actuator that isused.

The voltage control system for the piezoelectric motor 42 includes anelectronic system capable of handling the bandwidth required to move theactuator by its required distance, i.e., at least 0.006 inches, in onemillisecond or less. For example, a high voltage amplifier-based designtaking a control signal from an analog front end circuit can be used.The analog front end circuit can be either an analog control circuit ora digital control circuit that converts to analog through an analog todigital converter.

The current control system for the moving coil motor 62 is similar tothe voltage control system for the piezoelectric motor 42, except forthe addition of a feedback loop to monitor the current output of theamplifier stage, either through an analog circuit or a digital circuit.The feedback loop monitors the current and adjusts it to follow aproportional gain value to the control signal coming from the analogfront end circuit. If the current is too low, the feedback loopincreases the voltage until the appropriate current is reached.Likewise, if the current is too high, the voltage is decreased until thecorrect current level is reached.

Having described the electromechanical aspects for physically moving thegate 22, the portion of the system that governs how far the gate mustmove, and which direction it must move, will now be described.

In order to move the gate 22 and position the frames 40 in properregistration with respect to each other and the aperture 32, it isnecessary to determine the location of the frames once the film stopsmoving at the conclusion of each intermittent pull down by theintermittent sprocket 24. This determination of frame location from oneframe to the next will reveal the amount of misregistration that needsto be corrected. In accordance with the present invention, registrationinformation is applied to the film 10 corresponding to the location ofthe frames 40 on the film 10. This information is sensed or “read” inorder to determine the frame's location relative to the frame thatpreceded it.

In one form of the invention, the information is embodied in aregistration reference mark 76 adjacent to the frame 40. In thepreferred embodiment, there is at least one registration reference mark76 associated with each frame 40. By detecting the location of theregistration reference mark 76 and comparing its location relative tothe location of the immediately preceding registration reference mark,it is possible to determine the amount of movement necessary to correctmisregistration on a frame by frame basis. With this comparativeinformation, the difference between the locations of two successiveregistration reference marks 76 can be calculated and a signal sent tothe actuator commanding it to move the gate 22 so that the two marks layon top of each other. Once the registration reference marks 76 lay ontop of each other, then the frames 40 will also.

When the film registration process starts, the first frame 40 with aregistration reference mark 76 acts as a “benchmark” for the subsequentregistration of every frame 40 that follows. In other words, thelocation of the first frame 40 relative to the aperture 32 is determinedby sensing the location of a first registration reference markassociated with that first frame. The location of the next or secondregistration reference mark is also determined, and the gate 22 is movedso that the second mark lays on top of the first mark, at the samelocation as the first mark. Once the second registration reference markhas been aligned with the first registration reference mark (at the samelocation as the first registration reference mark), then the first andsecond frames will also be equally aligned or “registered.” By preciselyregistering subsequent frames 40 of the film “on top” of each other inthis manner, substantially all jitter and weave will be eliminated, andthe resolution of the projected image will be substantially enhanced.

It will be appreciated that, at the beginning of the registrationprocess, the first “benchmark” frame should be “centered” as much aspossible with respect to the aperture 32. In other words, the center ofthe first frame 40 should be aligned as much as possible with theoptical axis of the projector lens 36, which should also be in opticalalignment with the aperture 32. In this way, all subsequent frames 40,which are registered with respect to the first frame, will be equallyand correctly registered.

The registration references mark 76 can take a variety of differentforms. The main requirement of the registration reference mark 76 isthat it must be capable of being detected by a process that candetermine the location of the mark and then compare that location to thelocation of the previous mark. For example, a circle is capable offunctioning as one aspect of a registration reference mark. The circlecan be located by a sensor and then compared to the location of thecircle associated with the previous frame. Once the distance between thetwo circles and their direction relative to each other have beencalculated, the actuator can move the gate 22 by the correspondingdistance and direction to lay the two circles on top of each other inthe manner described above.

The registration reference mark 76 in accordance with one embodiment ofthe invention employs multiple shapes. As shown in FIG. 10, these shapesmay comprise geometric shapes, such as a square 78, a circle 80 and atriangle 82. The square 78, by definition, has a constant dimension onall four sides, i.e., from top to bottom and from side to side. Thecircle 80 is placed adjacent to the square 78 and is the geometric shapeused to calculate the amount of misregistration of each frame 40. Thediameter of the circle 80 is the same as the width of the square 78.Alternatively, a rectangle may be used instead of the square 78, so longas the width of the rectangle is the same as the diameter of the circle80. The triangle 82 is placed on the other side of the square 78 fromthe circle 80. The base of the triangle 82 is shown aligned with thebottom of the square 78 and has a length that is the same as the widthof the square, although triangles having other dimensions may be used.

If desired, the registration reference mark 76 may also includeadditional information. With reference again to FIG. 10, optionaladditional information is set forth to the left of the three geometricshapes. This other information may include, for example, binaryinformation 84 indicating the frame size, film speed, movie title, laborigin, or any other appropriate information. The binary information mayalso include information signaling the start 86 of the information bandat the beginning and a checksum 88 at the end. The type of message 90also may be provided. However, this additional information is not neededor used to determine the location of the frame 40. Rather, as set forthabove, frame location is determined by the three geometric shapes.

One aspect of the registration reference marks 76 involves the locationof these marks on the film 10 and the number of marks that are used.Preferably, there is one registration reference mark 76 associated witheach frame 40. In this way, each and every frame 40 will be preciselyregistered and resolution of the projected images will be maximized.Alternatively, registration reference marks 76 may be applied to everyother frame 40, or in some other number or convention, to achieve betterregistration and resolution than conventional systems, although not asgood as the resolution provided when each frame 40 is registered.

With respect to the location of the registration reference marks 76,each mark is preferably located on a portion of the film closelyadjacent to each frame 40. In one embodiment shown in FIG. 11, theregistration reference mark 76 is located in the longitudinal space 92between each frame 40. This space 92 is large enough to fit theregistration reference marks 76 in most film formats. The registrationreference marks 76 also could be located on the outside of the film'sperforations 94, or between the perforations. However, this is not apreferred location because it is ordinarily occupied by sound trackinformation.

In the alternative, the registration reference mark 76 may be locatedwithin the image itself, but this would require an image capture systemthat could scan an image and then interpret the location of the markfrom the entire frame 40. Accordingly, this approach has certaindrawbacks. The registration reference marks 76 also could be appliedwith ink or a magnetic charge that is invisible to the naked eye, butthat could be read by an appropriate sensor. However, the preferredlocation of the registration reference marks 76 is immediately outsidethe frame 40. By placing the registration reference marks 76 outside theframe 40, they can be read by the sensor without affecting the image tobe projected. The most preferred location of the registration referencemarks 76 is in the space 92 between each frame 40.

The registration reference marks 76 may be placed on the film 10 in anysuitable manner, preferably during the manufacture of IN's, IP's orother intermediate printing process, or in the equivalent digitalversion of that process (“digital intermediate”), wherein fades,dissolves, titles, effects, color “timing,” density corrections, andother intermediate processes are handled digitally before scanning backout to film. For example, the registration reference marks 76 may beapplied to the film by a laser device precisely mounted on a registeredcontact “step” printer. The precise method of mounting the laser deviceto such a printer will vary with the different types of printers, andvarious techniques exist to modify step printers for placement of suchlaser devices. Other suitable devices may be used to apply theregistration reference marks 76, in particular, the outline of the threegeometric shapes. Regardless of the device that is selected, it must beable to apply the registration reference marks 76 to the film 10 suchthat the square 78, circle 80 and triangle 82 are transparent andsurrounded or outlined by a non-transparent portion. Alternatively, thesquare 78, circle 80 and triangle 82 may be non-transparent andsurrounded or outlined by a transparent portion. Laser devices arecapable of providing these types of registration reference marks by useof appropriate masking and the like, but other suitable devices may beused as desired.

In applying the registration reference marks 76 to the film 10, it isimportant to position each registration reference mark in a locationthat most closely tracks the exposure of each frame 40 onto theintermediate film. Accordingly, each registration reference mark 76should be applied to the film 10 as close as possible to itscorresponding frame 40 and the operative registration pins of thecontact “step” printer. In this manner, the laser device, or othersuitable device, can precisely apply the registration reference marks 76in the same location as each frame 40 is exposed onto the intermediatefilm stock.

If the registration reference marks 76 are applied during the “digitalintermediate” process, the marks can be placed in the correct positionby means of the imaging computer and its associated software. They canthen be placed on the film elements generated thereby using the samefilm recorder technology as is used to duplicate the film imagesthemselves.

Alternatively, if the registration reference marks 76 are applied in thecontext of dye-transfer (imbibition, “IB”) printing (e.g. the originalTECHNICOLOR 3-strip process), the marks may be placed prior to makingthe separation matrixes, or otherwise as appropriate to insure that theymaintain alignment with the frames 40 themselves throughout theduplication process. The IB process is fully pin-registered, unlikestandard duplication using multi-layer Eastmancolor-type film.Therefore, the registration reference marks 76 applied in this instancewill have a less involved function, in that they need not be used tocorrect for printing misalignment, but function simply to insure correctprojector registration by compensating for any possible shrinkage,expansion or other such variables.

No matter how the registration reference marks 76 are applied, theyshould be placed in repeatable precise position relative to the frame40. In this regard, prior to the manufacture of release prints, theimage is still precisely located on the film 10 relative to theperforations. The subsequent process of high-speed contact printing willproduce errors in image placement relative to the film edges andperforations, for the reasons described above, such as the variablehigh-speed printer transport and inevitable misalignment of thebi-packed film moving through the printer. However, because theregistration reference marks 76 are aligned to the images themselves,they will be duplicated in the same manner, right next to theirrespective frame 40. Accordingly, one can still correctly position theimage by simply tracking the registration reference marks 76 and bymoving the gate 22 to correctly reposition the film 10 accordingly.Hence, even though the images may no longer be precisely locatedrelative to the perforations 94 and the film's edges, they will alwaysbe located with precise reference to their respective registrationreference marks 76. These registration reference marks 76, though theyare located between the projected frames 40 and thus will never appearon the screen, are duplicated with the images themselves during thehigh-speed contact printing process.

An appropriate sensor must be used to detect and “read” the registrationreference marks 76. Preferably, the sensor is fast-acting andtriggerable. The sensor also is one that preferably operates on theprinciple of detecting deviations between light and dark. For example,photocells can not only determine if something is light or dark, butalso shades of gray between the two. Solar cells can detect varyinglight levels and respond at very high speeds. Magnetic pickup heads canread a portion of the film 10 which has been coded, and this informationmay used to determine the film's location. For the reasons set forthbelow, LED and CCD technology is the currently preferred sensor-basedsystem, However, it will be understood that LED and CCD technology isnot the only suitable sensor system, and other types of suitable sensorsmay be used.

CCDs are well-known devices having defined pixels that can be exposed bylight and read digitally. They are not only very fast, but they alsoallow direct connection to most digital systems. Both an X and Y matrixCCD or line CCD are suitable. As shown in FIGS. 12-13, the differencebetween them is only in the number and arrangement of pixels. The matrixCCD 96, shown in FIG. 12, has a number of pixels 98 in both the X and Ydirections, resulting in an X-Y matrix. This type of CCD usually takeslonger to evaluate due to the larger number of pixels 98 on the cell.The line CCD 100, shown in FIG. 13, uses the same technology, but withonly a single row of pixels 98. This single row of pixels 98 is quickerto read and contains less data to sort and analyze.

In order for the line CCD array to work, the film 10 must be illuminatedto cast the outline of the three geometric shapes, i.e., the square 78,the circle 80 and the triangle 82, onto the CCD array 96 or 100. Thereare several options available to illuminate the film 10. Of course, theopening of the shutter will illuminate the mark 76 and thereby exposethe CCD. However, if the film 10 is moving while the shutter is open, itwill cause a blurring of the image on the screen, which is unacceptable.

Therefore, the registration reference mark 76 preferably is illuminatedwhile the shutter is closed so the corrective move can be completedbefore the shutter opens. One way to illuminate the registrationreference marks is by utilizing an LED array 102. This array can turn onbriefly and expose the CCD array 100 through the film 10 while theshutter is still closed. The LED array 102 may be either visible-lightbased or invisible-light based. The benefit of the invisible light arrayis that it prevents any bleed-through light from the LED array 102 frombeing projected and thus visible to the audience. For example, thisarray could flash 2.5 ms prior to the opening of the shutter, allowingenough time for the actuator to move the gate 22 before the shutteropens. The LED array 102 is the presently preferred way to illuminatethe CCD array 100.

One embodiment of the sensor, using arrays of LEDs and CCDs, isillustrated in FIGS. 14-16. In this embodiment, there are two sets ofarrays of LEDs 102 and CCDs 100, with one set above and one set belowthe aperture 32 in the aperture plate 30 of the projector 16. Thisarrangement provides redundancy and increased reliability when, forexample, there are two registration reference marks 76 associated witheach frame 40 and both sets of arrays 100 and 102 are in use.Alternatively, only one of the sets of arrays could be used, and if oneof the sets malfunctioned, the other set could be activated to keep thesystem operating. However, it is not necessary or required to usemultiple sets of LED and CCD arrays. Therefore, FIGS. 14-16 will bediscussed with reference to only one of the LED/CCD arrays, and it willbe understood that the description applies equally to both sets ofarrays.

FIG. 14 is a rear elevational view of the projector gate 22, and FIG. 15is an elevational side view of the projector gate taken along the lineA-A of FIG. 16, which is a front elevational view of the projector gate.Before discussing the LED/CCD arrays 100 and 102, the piezoelectricmotor flexure stage 46 shown in FIGS. 14-16 will be discussed briefly.As shown in these drawings, the stage 46 has its moveable inner frame 50connected to the projector gate 22, which has been disconnected from itsconventional projector support structure. The inner frame 50 may beconnected to the gate 22 in any suitable manner, such as by bolts,screws or the like that will provide a secure connection between theinner frame of the stage and the gate. The outer frame 48 of the stage46 surrounds the inner frame 50 and is connected to the adjacentprojector structure that is fixed against movement relative to the gate22. Thus, movement of the inner frame 50 of the stage 46 will result incorresponding movement of the gate 22, in accordance with the principlesof the invention.

There is an LED array 102 on the front side of the gate 22, which is tothe right in FIG. 15. This array 102 is adapted to transmit lightthrough an aperture in the gate 22 and another aperture 32 in theaperture plate 30 so that light from the LED array 102 passes throughthe film 10 when the film is stopped in the gate 22 during theintermittent pulldown. Thus, once the film 10 has stopped in the gate22, the LED array 102 is quickly activated to pass light through theregistration reference mark 76 associated with the frame 40 that isabout to be projected. As a result, certain pixels 98 in the CCD array100 will be illuminated and others will not, depending on whether thegeometric shapes are transparent or non-transparent. In either case, thelight will pass through the film 10 to the back side of the gate 22,which is to the left in FIG. 15.

With reference to FIGS. 14 and 15, as the light passes horizontallythrough the film 10, the light that passes through the registrationreference mark 76 is received by a first mirror 104. As shown in FIG.14, this first mirror 104 reflects the light vertically downwardlytoward a second mirror 106. The reference numeral 108 represents theline of travel of the light, and the reference numeral 110 representsthe band of the total light that is transmitted. The second mirror 106then reflects the transmitted light along a generally horizontal pathoutwardly to one side of the aperture 32, where it is received by theCCD array 100. As a result, the transmitted light will illuminatecertain pixels 98 in the CCD array 100. With this information, thelocation of the registration reference mark 76 can be determined.

In the first step of this determination, the number of pixels 98illuminated in the CCD array 100 by the first registration referencemark 76 (associated with the first frame) establishes the “benchmark”for the registration of all subsequent frames 40. As noted previously,this “benchmark” frame should be centered as much as possible withrespect to the optical axis of the projector lens 36. With thisinformation, the location of the first registration reference 76 markwith respect to the aperture 32 is determined. This location willcorrespond to the center of the circle 80 and the geometric center ofthe square 78 for all future calculations. In other words, this will bethe location of a frame 40 that is properly registered with respect tothe aperture 32.

When the LED array 102 is activated again for the next succeeding frame40, the light passes through the registration reference mark 76associated with that frame and certain pixels 98 of the CCD array 100are illuminated again. The number of pixels 98 illuminated by the circle80 are compared to the number of pixels 98 illuminated by the square 78.As shown in FIG. 17, if the number of pixels 98 illuminated by thesquare 78 and the circle 80 are equal (i.e., when W₁=W₂), then the CCDarray 100 necessarily falls directly through the center of the circle 80and the geometric mid-point of the square 78, meaning that the frame 40is properly registered in the Y direction with respect to the aperture32 and no corrective movement in the Y direction is required. However,when the number of pixels 98 illuminated by the circle 80 is less thanthe number illuminated by the square 78 (i.e., when W₂<W₁), as shown inFIG. 18, then the frame 40 is misregistered with respect to the aperture32 and gate movement in the Y direction is required to properly registerthe frame.

To determine whether the CCD array 100 is located above or below thecenter of the circle 80, the pixels 98 illuminated by the triangle 82are also read. Depending on the number of pixels 98 that are illuminatedby the triangle 82, it can be determined whether the frame 40 needs tobe moved in the positive Y direction or the negative Y direction toachieve proper registration of the frame. For example, if the number ofpixels 98 illuminated by the triangle 82 is above a certain value, thenit can be determined that the CCD array 100 is located below the centerof the circle 80. Thus, by comparing all of the CCD array data generatedfrom each geometric shape, it is possible to determine the amount ofmovement and the direction of movement necessary to properly registereach frame 40.

FIG. 19 helps illustrate the calculations associated with the circle 80that need to be made to determine the extent of any misregistration inthe Y direction. In FIG. 19, D_(c) represents the diameter of the circle80 and the width of the square 78. L_(c) represents the length of achord of the circle 80 and the location of the CCD array 100 relative tothe center of the circle. Y_(d) represents the offset of the CCD array100 in the Y direction, as measured from the center of the circle 80. Rrepresents the radius of the circle 80, or ½ of D_(c). To calculate theamount of misregistration in the Y direction, simple mathematics usingthe Pythagorean theorem is used according to the following equation,where Y_(d) equals the amount of misregistration in the Y direction:$Y_{d} = \sqrt{\left( \frac{D_{C}}{2} \right)^{2} - \left( \frac{L_{C}}{2} \right)^{2}}$

To calculate the amount of misregistration in the X direction, it isnecessary simply to know the location (i.e., the pixel) on the CCD array100 corresponding to the center of the circle 80 of the firstregistration reference mark 76. This location will correspond to thecenter of the circle 80 and the midpoint on the CCD array 100 for allsubsequent circles. When light from the LED array 102 passes throughsubsequent circles 80 and illuminates the CCD array 100, the midpoint ofthe chord Lc for those circles will be calculated and compared to themidpoint of the CCD array 100 as determined by the first circle 80. Ifthere is a difference between the midpoint of a subsequent circle 80 andthe midpoint of the CCD array 100, then the amount of misregistration inthe X direction can be calculated based on the difference in distancebetween these two points.

In view of the above, it will be appreciated that the CCD array also canbe configured to act as the “benchmark” for the registration of theframes 40, in conjunction with the registration reference marks 76. Forexample, a predefined location on the CCD array can be selected as thelocation to which all frames will be moved. By using the registrationreference marks 76 to move all frames 40 a predefined location on theCCD array, the undesirable jitter and weave will be eliminated.

One of the advantages of using geometric shapes to comprise theregistration reference mark 76 is that fluctuations that occur duringthe film production process, or fluctuations in the illumination of themarks, will not affect the results of the gate movement calculations.For example, if film exposure and reprinting makes the square 78 smalleror larger than its original size, the circle 80 and triangle 82 willchange in size by the exact same ratio. Furthermore, lower or higherpower illumination will not affect the ability to calculate the centerof the circle 80 because of the corrective nature of the other twogeometric shapes, namely the square 78 and the triangle 82.

Another possible way to illuminate the CCD array 100, shown in FIG. 20,is to provide a notch 112 in the shutter 114 in a way that allowsexposure of the CCD array 100 before the shutter opens. However, thismethod may cause a ghosting image across the film while the notch 112moves across the film frame 40, which would be unacceptable.

Alternatively, light from the lamp house 34 may be directed around thefilm 10 and used to expose the registration reference mark 76 while theshutter is closed, as shown in FIG. 21. This system would requiremirrors 116 or a light pipe, for example, to channel the light to theappropriate location.

Each of the registration reference marks 76 is read by the sensor assoon as the film 10 has stopped in the gate 22. However, sensing theregistration reference marks 76 at a different time is possible andopens some advanced processing possibilities. For example, if theregistration reference mark 76 is sensed before the frame 40 associatedwith that mark has stopped in the gate 22, a period of time longer than1.5 milliseconds can be used to analyze the mark. By increasing the timeavailable for analysis, a slower, less expensive registration processor(discussed below) may be used. Moreover, if the registration referencemark 76 can be read and analyzed before the frame 40 is stopped in thegate 22, the gate can be commanded to move toward the correct positionduring the pull down of the frame by the intermittent sprocket 24. Thiswould allow approximately 10 milliseconds of time to move the gate 22instead of 1 millisecond or less if the registration reference mark 76is not read until the film 10 fully stops in the gate 22.

In another aspect of the invention, corrective gate movement could be atleast partially determined by searching for and determining theexistence of a trend of misregistration of the film 10 from one frame 40to the next. Based on the nature of the “trending,” basic correctivegate movements could be predicted and executed. While a trending systemdoes not cancel all error when the film 10 stops, it should at leasteliminate the errors associated with the film duplication process. Byanalyzing how several successive frames 40 have stopped in the gate 22,a film stop deviation may be trended and corrected by appropriate gatemovement. Although this method could possibly correct for the majordeviations causing misregistration of the frames 40, it is unlikely tobe as accurate as analyzing the registration reference marks 76 once thefilm 10 has stopped in the gate 22 and before the shutter 114 hasopened.

In accordance with the invention, a registration processor 118 governsthe operation of the system. With reference to FIG. 22, the registrationprocessor 118 communicates with a host processor 120 to receiveinformation related to film format (e.g., a four-perforation per frameformat or a three-perforation per frame format), frame rate, brightness,and so forth. The host processor 120, in turn, communicates with amotion processor 122 that controls operation of the projector 16. Thehost processor 120 will inform the registration processor 118 if thefilm 10 contains registration reference marks 76 and, if so, the type ofregistration reference marks being used. The connection between the hostprocessor 120 and the registration processor 118 also will provide aline of communication for determining registration status and correctoperation.

Upon a command from the host processor 120, the registration processor118 commences its operation to precisely register the frames 40. Theregistration processor 118 will activate the LED array 102, for example,to illuminate the registration reference marks 76 which, in turn,project the outline of the three geometric shapes onto the sensor, suchas a line CCD array 100, in the manner described above. The registrationprocessor 118 then analyzes the pixel information gathered from thesensor, sorts through the information and determines the location of theframe 40 being registered relative to the previous frame. Once thisinformation is known, the registration processor calculates thedistance, in both the X direction and the Y direction, by which theframe 40 is misregistered with respect to the previous frame. Thiscalculation can be in the form of a vector direction and length, whichdetermines the corrective direction and distance needed to move the gate22.

Depending upon the direction and the length of the vector, the amount ofvoltage or other signal needed to move the gate 22 in the X directionand/or the Y direction is calculated. A command signal containing thenecessary information is then transferred to an actuator processor anddriver 124 to generate an appropriate signal. For example, if theactuator is the piezoelectric motor 42, then the signal will be avoltage signal. The actuator processor and driver 124 amplifies thevoltage signal to produce a precise voltage that is applied, forexample, through the cable 60 to the piezoelectric motor flexure stage46, which then moves the gate 22 in the X and/or Y directions to movethe frame 40 into precise alignment with respect to the previous frame.

The registration processor 118 may take several forms. For example,commercially available microprocessors, digital signal processors,microcontrollers, analog circuits and other suitable processors may beused. In addition, a combination of these various types of processorscan be used to determine and send the corrective move signal to theactuator.

In other aspects of the invention, the registration processor 118 maydefault to a lower level of frame registration accuracy, as may beappropriate. For example, if the host processor 120 informs theregistration processor 118 that the film 10 in the projector 16 does nothave registration reference marks 76, the registration processor 118 maydefault to a mode in which the sensor reads the position of perforations94 instead of registration reference marks 76 on the film 10. In thisdefault mode, the sensor would determine the location of a particularperforation 94 associated with a frame 40 and place each successiveperforation (associated with each successive frame) in overlappingrelation to the one that preceded it. Even though this default modewould be less accurate than systems that read the registration referencemarks 76, an increase in film registration accuracy nevertheless can beachieved as compared to conventional projectors having no such system.

In another more detailed aspect of the invention, information regardingthe location of the registration reference marks 76 and thecorresponding corrective movements of the gate 22 may be analyzed andstored in the registration processor 118. By analyzing and storing thisinformation for enough frames 40, the registration processor 118 mayprovide an estimate of the corrective move that will be required beforea frame 40 enters the gate 22. This provides several advantages.

First, as mentioned previously, this “trending” allows movement of thegate 22 prior to the correct analysis as the frame 40 is being pulledinto the gate. This minimizes the distance the gate 22 has to move oncethe actual move has been calculated. If the majority of themisregistration can be corrected by gate movement during the actualpulldown of the frame 40 into the gate 22, then only a minor correctionwill be necessary once the film 10 has stopped moving. Accordingly, ifthe distance of this final corrective move is small, it can be performedmore quickly than a longer corrective move.

Second, this trending allows corrective moves to be made with respect tofilm frames 40 that do not have any registration reference marks 76, orwhere the registration reference marks have been corrupted in some wayand cannot be read. For example, if the film 10 is damaged or dust orother contaminants obliterate a registration reference mark 76, eitherin whole or in part, it may not be possible to read the registrationreference mark. In these circumstances, an accurate determination of thecorrective action necessary with respect to that particular frame 40will not be possible. However, instead of bypassing corrective actionwith respect to this frame 40 altogether, the trend in misregistrationof the immediately preceding frames will allow the registrationprocessor 118 to predict the proper location of the film frame 40 tocorrect for as much misregistration as possible.

As an additional feature, the design of the gate 22, in conjunction withthe motion processor 122 and the registration processor 118, may includea system to permit high-speed computer control over the resistance tofilm movement in the gate. For example, after the film 10 has stopped inthe gate 22, the resistance may be decreased to provide a low startingfriction component when the film is pulled down by the intermittentsprocket 24. This reduced gate friction would allow lower peakintermittent sprocket torque and would reduce the stresses placed on thefilm 10 by the gate 22 during the intermittent pull down move. Near theend of the intermittent pull down move, appropriate friction necessaryto stop the film 10 may be reapplied back to the gate 22. This repeatedcycle of decreasing and increasing gate friction would accomplish theobjectives of stopping the film 10 accurately at the end of eachpulldown move, while reducing the work required to move the film at thebeginning of each move.

In view of the foregoing, it will be appreciated that the principles ofthe present invention can be applied in numerous ways to eliminatejitter and weave. For example, instead of using the registrationreference marks 76 to move the gate 22, these marks can be used tomanipulate other components in the projector as appropriate to eliminatethe jitter and weave. These manipulations can be accomplished bymechanical, optical and other appropriate means. Therefore, while aparticular form of the invention has been illustrated and described, itwill be apparent that various modifications can be made withoutdeparting from the spirit and scope of the invention. Accordingly, it isnot intended that the invention be limited, accept as by the appendedclaims.

1. A method of registering frames of film with respect to an aperture ina motion picture projector, comprising: a. applying registrationinformation to the film corresponding to the location of the frames onthe film; b. moving the film through the projector and intermittentlystopping the film frame-by-frame with respect to the aperture; c.reading the registration information associated with each frame prior toprojection to determine the location of the frame with respect to theaperture; d. determining the amount of correction that is necessary toachieve proper registration of the frame with respect to the apertureprior to projection; and e. moving the frame into proper registrationwith respect to the aperture prior to projection.
 2. A system forregistering frames of film in a motion picture film projector having agate for receiving film during intermittent advancement of the filmthrough the projector, comprising: a. an actuator connected to the gatethat is adapted to move the gate relative to the aperture; b. a sensorthat reads registration information on the film associated with eachframe to determine the location of the frame with respect to theaperture prior to projection; and c. a registration processor connectedto the sensor and the actuator that is adapted to determine the amountof movement that is necessary to move the gate and thus the frame intoproper registration with respect to the aperture.
 3. The system of claim2, wherein the actuator comprises a piezoelectric motor.
 4. The systemof claim 2, wherein the actuator comprises a piezoelectric motor flexurestage.
 5. The system of claim 2, wherein the actuator comprises a movingcoil motor.
 6. The system of claim 2, wherein the registrationinformation applied to the film comprises a registration reference markthat is read by the sensor.
 7. The system of claim 6, wherein theregistration reference mark comprises a plurality of geometric shapes.8. The system of claim 7, wherein the geometric shapes comprise at leasta circle and square.
 9. The system of claim 8, wherein the geometricshapes further comprise a triangle.
 10. The system of claim 2, whereinthe registration information is applied to the film in a space betweenadjacent frames on the film.
 11. The system of claim 2, wherein thesensor comprises a light-based sensor.
 12. The system of claim 11,wherein the light-based sensor comprises an LED array and a CCD array.13. The system of claim 12, wherein the light-based sensor furthercomprises a mirror for reflecting light transmitted from the LED arrayonto the CCD array.
 14. The system of claim 2, further comprisingredundant sensors adapted to read redundant registration informationassociated with each frame.
 15. The system of claim 2, wherein theregistration processor controls operation of the sensor and processesthe registration information for each frame to determine the location ofsuccessive frames relative to the aperture.
 16. The system of claim 15,wherein the registration processor further determines the amount of filmmisregistration from one frame to the next and generates an outputsignal that is delivered to the actuator, and wherein the output signalcommands the actuator to move the gate such that the frames arecorrectly registered with respect to the aperture.
 17. The system ofclaim 16, wherein the output signal is a voltage based signal.
 18. Thesystem of claim 16, wherein the output signal is a current based signal.19. The system of claim 2, wherein the actuator is configured to movethe gate in increments as small as approximately 0.000002 inches inabout one millisecond or less.
 20. The system of claim 2, wherein theactuator and gate are configured such that the actuator can move thegate at least 0.006 inches in both the X direction and the Y direction.21. A device for registering motion picture film in a projector,comprising: a. a gate for receiving film and intermittently stoppingframes of the film relative to an aperture, wherein the gate is moveablewith respect to the aperture; b. an actuator connected to the gate,wherein the actuator is configured to move the gate relative to theaperture; and c. a processor that commands the actuator to move the gaterelative to the aperture based on registration information on the filmadjacent to the frames.
 22. Motion picture film, comprising: a. a lengthof motion picture film having a plurality of projectable images on thefilm, wherein each image is defined by a frame; and b. registrationinformation applied to the film adjacent to a plurality of the frames,wherein the registration information is located in the same positionrelative to each of the frames.
 23. The motion picture film of claim 22,wherein the registration information comprises information that iscapable of being read by a sensor.
 24. The motion picture film of claim23, wherein the registration information comprises a plurality ofdifferent shapes that are read by a light-based sensor.
 25. The motionpicture film of claim 24, wherein the plurality of different shapescomprises at least a circle and a square or rectangle, and wherein thediameter of the circle is equal to the width of the square or rectangle.26. The motion picture film of claim 25, wherein the plurality ofdifferent shapes further comprises a triangle adjacent to the circle andthe square or rectangle.
 27. The motion picture film of claim 22,wherein the registration information is located outside the frame. 28.The motion picture film of claim 26, wherein the registrationinformation is located in the space between adjacent frames.
 29. Themotion picture film of claim 22, wherein redundant registrationinformation is applied to the film for each frame.